EFFECT OF SERINE AND ETHANOLAMINE ADMINISTRATION ON PHOSPHOLIPID-RELATED COMPOUNDS AND NEUROTRANSMITTER AMINO-ACIDS IN THE RABBIT HIPPOCAMPUS

The report concerns mechanisms for the increase of extracellular level s of ethanolamine and phosphoethanolamine in CNS regions, such as the hippocampus, in transient brain ischemia, hypoglycemia, seizures, etc. L-Serine (2.5-10 mM), D-serine (10 mM), or ethanolamine (10 mM) was a dministered for 20 min via a microdialysis tubing to the hippocampus o f unanesthetized rabbits. The concentrations of primary amines were de termined in the dialysates. When levels were elevated 10-100 times in the extracellular fluid, L-serine caused a dose-dependent increase of the concentration of extracellular ethanolamine. Ethanolamine caused a corresponding, although somewhat smaller, increase in serine levels. Furthermore, L-serine also induced an increased concentration of phosp hoethanolamine that was delayed in time relative to the peak of ethano lamine. D-Serine was as effective as L-serine in raising ethanolamine levels but had no effect on phosphoethanolamine. Ethanolamine, but not L-serine, also increased extracellular glutamate/aspartate levels in an MK-801-dependent fashion. A similar effect, but delayed in time, wa s observed with D-serine. These effects were inhibited by MK-801, The concentrations of other amino acids were not significantly affected. T he characteristics of the effects are suggestive of base exchange reac tions between serine and ethanolamine and between ethanolamine and ser ine glycerophospholipids, respectively, in neuronal plasma membranes.